1. Field of the Invention
The present invention relates to a multilayer composite including an insulating substrate and patterned conductive layers and insulating layers alternately laminated on the insulating substrate, and a method for preparing the multilayer composite.
2. Description of the Related Art
A conventional electronic component is a multilayer composite including an insulating substrate and patterned conductive layers and insulating layers alternately laminated on the insulating substrate. For example, Japanese Unexamined Patent Application Publication Nos. 2002-26530 and 2001-210141 disclose a method for preparing such a multilayer composite. Referring to FIG. 2A, a patterned conductive layer 21 is made of, for example, a conductive paste on an insulating substrate 20. This patterned conductive layer 21 is fired and then cooled together with the insulating substrate 20. The patterned conductive layer 21 contracts during firing, and the insulating substrate 20 and the patterned conductive layer 21 contract during cooling. The patterned conductive layer 21 has a higher thermal expansion coefficient than the insulating substrate 20. Therefore, the patterned conductive layer 21 contracts more than the insulating substrate 20. The difference in thermal contraction between the insulating substrate 20 and the patterned conductive layer 21 produces a tensile stress in the patterned conductive layer 21. Referring to FIG. 2B, this tensile stress causes the laminate including the insulating substrate 20 and the patterned conductive layer 21 to be warped and concave.
Referring then to FIG. 2C, an insulating layer 22 is laminated on the top of the patterned conductive layer 21. The insulating layer 22 is also fired and cooled. The insulating layer 22 contracts during firing, and the insulating substrate 20 and the insulating layer 22 contract during cooling. As described above, the patterned conductive layer 21 has a higher thermal expansion coefficient than the insulating substrate 20. Such a thermal expansion coefficient produces a tensile stress in the patterned conductive layer 21 and causes the laminate to be warped and concave. In contrast, the insulating layer 22 may have a sufficiently lower thermal expansion coefficient than the insulating substrate 20. Such a thermal expansion coefficient produces a compressive stress in the insulating layer 22. This compressive stress causes the laminate to be warped and convex. Therefore, the compressive stress in the insulating layer 22 cancels the tensile stress in the patterned conductive layer 21. The composition of the insulating layer 22 is determined according to these stresses. Thus, the warpage of the laminate is almost completely corrected.
Referring to FIG. 2D, subsequently, further patterned conductive layers 21 and insulating layers 22 are alternately laminated on the laminate to form a multilayer composite 23. All the insulating layers 22 include the same insulating materials.
As described above, the composition of the insulating layers 22 is determined so as to prevent warpage of the laminate. Nevertheless, the insulating layers 22 cannot completely correct the warpage of the laminate for various reasons, such as variations in the purity of the materials of the insulating layer 22 and problems associated with its preparing equipment. Referring to FIG. 2D, therefore, the laminate, including many patterned conductive layers 21 and insulating layers 22, exhibits a noticeable warpage.
Such a warped laminate presents various problems. For example, a warped bottom surface of the laminate makes it difficult to fix the laminate at a predetermined position for laminating the patterned conductive layers 21. Such a surface also prevents precise formation of the patterned conductive layer 21.
Many multilayer composites 23 can be prepared at the same time using, for example, a mother insulating substrate for forming a plurality of insulating substrates 20. The patterned conductive layers 21 and the insulating layers 22 are alternately laminated on individual areas of the mother substrate at the same time. Each area corresponds to one multilayer composite 23. The individual areas are then separated to form many multilayer composites 23. In this case, a laminate including the mother substrate, the patterned conductive layers 21, and the insulating layers 22 exhibits a noticeable warpage. This warpage, consequently, makes it difficult to fix the laminate or laminate the patterned conductive layers 21 precisely on the laminate. In addition, the laminate cannot be precisely divided into the multilayer composites 23, which, therefore, include many defective products. This results in a decrease in the yield of the multilayer composites 23.